I think you can make a hologram that well represents a dead person if you have enough data and biographical information on hand - in fact its the plot of one of my episode ideas where an ensign secretly replicates the holo-emitter and creates a hologram of his dead girlfriend who is unaware she's a hologram as is everybody else. But the fact that the Moset hologram started to exhibit traits of the real Moset out of nowhere pissed me off and seemed unrealistic and lazy.